14 DAY TRIAL // For long time, the moon was seen as a dead object, where, except for the occasional errant comet or asteroid impact, nothing has occurred for three billions of years.
However, recent research reveals a moon location where some kind of volcanic eruptions could have taken place within a very recent geologic time, as recent as 2 to 10 million years ago. The fresh "scars" on the moon's face might have been created by gas from inner moon which erupted through deep fractures. "That would make the features relatively young, since any time less than ten million years ago is "like yesterday" in comparison to the moon's age," said Peter H. Schultz, a planetary geologist at Brown University in Providence, Rhode Island.
Primarily, the moon's surface is marked by ancient remains of volcanic or impact events, wrapped over billions of years by space dust. The lack of atmosphere makes the moon very vulnerable to space debris that easily reaches its surface, creating continuously impact craters. Over hundreds of millions of years, bombardment by space debris eroded moon's surface like water erodes Earth's mountains.
In 1971, scientists spotted an 8-square-kilometer D-shaped area called the Ina structure, containing jagged and relatively dust-free volcanic rocks. Ina's images showed only two impact craters inside the structure, far less than the average for a similar moon surface, and features still sharp with little erosion. Measuring Ina's deposits reflected light wavelength compared to other moon parts with newly formed craters of a known age, the team noticed an exceptionally young age, of about 2 million years.
Light reflects at different wavelengths from recently disturbed images, so spectral data images indicate when and where changes on the moon's surface occur. "The color distinctions of the Ina structure show that the area is fresh compared to other sites," Schultz says. Ina's floor is covered with titanium-rich basalt, of blue spectral color, but the region is also strewn with green, the color of less mature dirt.
Researchers suppose that the moon still periodically erupts volcanic dust and gases, which could explain the Ina event. The volcanic moon eruptions blew off the previous rock, leaving behind less weathered rock. Ina's geology, at the intersection of two valleys, seems to resemble Earth's geologically active areas, like Africa's Great Rift Valley.
The team has identified other four to ten similar moon sites and they could still be active. "Most [moon] craters are degraded," Schultz added. "These [Ina features] are not degraded. It's a surface that has been recently formed or exposed."
"The force probably blew the dirt straight up and it either came right back down or fell to the side," says University of Hawaii lunar expert Jeff Taylor. "Such poofs of erupting gas might be the only source of wind on the moon's surface," he adds. "It's like a Steam eruption, but with no water vapor."
The nature of the gases involved in the eruptions remains unknown: radon, hydrogen and carbon monoxide are among the suspects. The puzzle, Schultz said, "may hold clues for the formation of the moon and even the early history of the Earth."
"Such features will clearly be targets of interest to see how often the moon burps and what deposits may have been left." Taylor said: "I think the biggest thing is that [this study] says the moon is not quite the dead object that many people think."
Paul Spudis, a planetary geologist at the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, says the scientists have "known for some time that the moon's not totally dead," because of the existence of moonquakes (like earthquakes). Also, previously, astronauts discovered proofs of gas bursts. "The significance of this research, Spudis says, is that it ties those earlier observations to a known surface feature."
Image credit: Peter H. Schultz